Insights into efficiency of sulphate reduction and microbial community in suspended fillers sequencing batch anaerobic biosystems under nutrient-poor conditions

Anaerobic biological treatment of sulphate - laden wastewater has been proven to be a feasible approach. However, it encounters formidable challenges when applied under nutrient - poor conditions. The efficacy of suspended fillers in augmenting microbial concentrations and enhancing the removal of contaminants had been empirically validated. However, there is limited research on the enhancement of sulphate removal by suspended fillers, and the enhancement mechanism remains unclear. Thus, suspended fill anaerobic bioreactor systems were established to investigate its feasibility under nutrient-poor conditions, and the enhancement mechanisms were further explored. The findings demonstrated that the presence of suspended fillers enabled anaerobic systems to achieve a sulphate removal efficiency of approximately 68.9%, even when the organic load rate was as low as 0.08 gCOD·(L·d)^-1. The Principal Coordinates Analysis results clearly demonstrated differences in community composition between sludge and filler samples at each stage (<i>R</i> > 0, <i>P</i> < 0.05). Further analysis of community composition revealed that <i>Desulfobulbus</i> and <i>Desulfobacter</i>, which were closely associated with sulphate removal, exhibited higher relative abundances in the filler samples compared to the sludge samples. Furthermore, the functional genes associated with sulphate removal were found to exhibit more pronounced expression in the sample of fillers. These findings suggested that the presence of suspended fillers creates a favourable environment for certain microorganisms, particularly some sulphate-reducing bacteria, enhancing microbial activity and increasing sulphate removal efficiency.